As one of conventional sterilization methods, a method of bringing a sterilization target into contact with an oxidizer such as hydrogen peroxide and then irradiating the sterilization target with light of 400 nm to 1000 nm has been known (for example, see Patent Literature 1). According to the method, hydroxy radicals are generated by irradiating the hydrogen peroxide with the light of 400 nm to 1000 nm, and the sterilization is attained by the thus-generated hydroxy radials.